This invention relates generally to an electrophotographic printing machine, and more particularly concerns an improved apparatus for supporting an endless belt arranged to move in a recirculating path.
In an electrophotographic printing machine, a photoconductive belt is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive belt is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive belt selectively dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive belt corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive belt, the latent image is developed by bringing a developer mix into contact therewith. Generally, the developer mix comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive belt. The toner powder image is then transferred from the photoconductive surface to a copy sheet. Finally, the copy sheet is heated to permanently affix the toner particles thereto in image configuration. This general approach was originally disclosed by Carlson in U.S. Pat. No. 2,297,691 and, has been further amplified and described by many related patents in the art.
Inasmuch as the photoconductive belt must be replaced periodically, it is necessary to have some technique for readily removing the belt from the printing machine. Thus, not only must the belt be easily removed by retracting one or more of the supports but, the supports must apply a substantially uniform tension to the belt during its operation. Various tensioning devices for endless belts typically distribute their loads uniformly across the width by a spring acting through a gimballed yoke. However, the cost and space allocation of such devices can become exorbitant. Moreover, since the idler roll of the device must be straddled by the yoke, the gimbal pivot frequently lies off the roller axis. The lateral forces created by the belt produce a tilting moment which, in turn, gives rise to non-uniform tension.
Accordingly, it is a primary object of the present invention to improve the system for applying a substantially uniform tension force to a photoconductive belt employed in an electrophotographic printing machine.